It is common practice to package, within cartons for food products, coupons of various sorts, and this is usually done for promotional purposes. It is desirable to assemble the coupon and the carton at the point of manufacture of the latter, because this saves the step of subsequent insertion of the coupon, which would normally have to be performed by the food packer. To enable assembly at the point of carton production, it is necessary that the coupon be adhered to the carton, and this must be done with a very specialized adhesive.
More particularly, the adhesive must be sufficiently tacky in the wet state to maintain the coupon on the carton at the time of initial assembly, and to withstand relatively high machine speeds; reducing production rates to accommodate coupon attachment is, of course, undesirable. The adhesive must also exhibit sufficient strength in the dry state so that the coupon does not become displaced or detached during subsequent setting-up operations for the carton, and during insertion of the contained product. On the other hand, the material must possess such release properties as will permit the consumer to remove the coupon without damage to it or the carton. Finally, after removal the adhesive should exhibit low levels of tack, so that the consumer can collect a number of coupons in a stack; adhesion under such circumstances would be a source of considerable annoyance.
Adhesives for this purpose have been developed in the past. However, as fas as is known, no such adhesive has heretofore been provided, which affords the desired balance of properties for virtually universal application to conventional carton materials. More particularly, cartons are typically fabricated not only from uncoated paperboard, but also from stock that has been coated in one way or another with such materials as low-density polyethylene, waxes (e.g., blends of paraffin and microcrystalline types), and nitrocellulose varnishes. Hence, the ideal adhesive would be capable of securing a coupon to a carton produced from any of the foregoing types of stock.
One prior art composition formulation is known, which consists of an aqueous dispersion of about 78.5 percent of a butyl rubber (i.e., isobutylene/isoprene copolymer) latex (containing about 63 percent solids), about 1.5 percent of a thickener (containing about 14 percent solids), and about 20 percent of a paraffin wax dispersion (containing about 40 percent solids). While the foregoing formulation is satisfactory for use in connection with uncoated paperboard, adhesion to stock having a surface of polyethylene, varnish or wax is found to be inadequate. Moreover, even as applied to uncoated board, the levels of initial adhesion tend to be somewhat deficient, necessitating a significant reduction in carton making machine speeds.
Accordingly, it is an object of the present invention to provide an adhesive formulation possessing an optimum balance of wet strength, dry strength, release characteristics and freedom from tack in the dry state.
It is also an object of the invention to provide an adhesive having the foregoing balance of properties, and exhibiting them as applied to carton stock having a variety of conventional surface compositions.
Another object is to provide such an adhesive which is of relatively simple composition, and is economical to produce.